This applicationis for the renewal of a program project that was initiated in 1986. The proposed research is the outgrowth of the program's progressd uring the current funding period,a nd consists of four projects and two supporting cores focused on the central theme of the structure/function of cardiac glycoside-sensitive proteins. The participating investigators with expertise in membrane biochemistry, protein chemistry, molecular genetics, cell biology,and cardiac physiology/pharmacology will combine their efforts to conduct the following studies: The first Project deals with the characterization of ion pumping and signal transducing functions of a pool of cardiac Na+/K+-ATPase that is localized in the caveolae microdomains of the cell membrane, the cardiacglycoside-induced traffic of signaling proteins into and out of cardiac caveolae, and the functional consequences of this altered traffic. The next Project proposes studies on the structure/function relationship and the reaction mechanism of a humann on-gastric H+/K+-ATPase that is sensitive to cardiac glycosides and is involved in ion homeostasis. Also proposed are studies on the functional characterization of a newly discovered muscle-specific member of the beta-subunit family of P-ATPases. Studies of the next Project are aimed at the identification of organized signaling complexes formed between Na and its close neighbors,the nature of the intermolecular domain interactions, and the cardiac glycoside-induced changes in these interactions and the resulting functions. The final Project proposes studies aimed at the characterization of the mechanisms and the pathways that link cardiac glycoside interaction with Na ATPase to the cardiac mitochondrial KATP channels, and the protective role of these pathways against ischemic damage. The proposed studies are expected to expand knowledge on the biological role of cardiac Na+/K+-ATPase in previously unexplored directions, and to provide new information on the basis of which the therapeutic value of cardiac glycosides as drugs, and their postulated hormonal roles, may be evaluated.